Over the past two decades, the dental profession has been urged to provide its clients with natural looking fillings for posterior teeth. Composite resins have been used to provide these natural looking fillings. Composite resins, when cured, have a natural tooth colour, can be placed in one appointment and are free of the toxin mercury.
Before placement, composite resins have a soft putty-like consistency and are generally non-compactable. Fillings formed of composite resin are cured by application of a concentrated source of light. To place a composite resin filling, a matrix is used. A matrix is a device which wraps around a prepared tooth area. It acts as a mold and limits the spread of filling materials beyond desired borders. This mold conforms ideally to the original anatomy of the interproximal tooth structure. Matrices are generally formed from stainless steel or plastic and can be circumferential or sectional. Circumferential matrices fit around the entire circumference of the tooth whereas sectional matrices fit only in one interproximal area of the tooth. Matrices are secured in place by use of wedges and/or clamps. Wedges are triangular in cross section and taper along their length. They are placed between the matrix and the adjacent tooth in order to seal the matrix against the base of the prepared tooth structure. Wedges are generally made of wood or plastic.
The placement of composite resin fillings in the interproximal area has been found to be very problematic. Since the resin is non-compactable, it is very difficult to create a firm contact point between the newly placed filling and the adjacent tooth. The contact point is the point at which the crown of one tooth contacts, or nearly contacts, the crown of an adjacent tooth. If a gap is formed at the contact point, food becomes trapped between the teeth causing gum irritation or inflammation, tooth movement and general patient dissatisfaction. When the curing light source is applied from the direction of the biting surface, this causes the resin material to be drawn away from the base of the proximal tooth preparation and towards the light. When this occurs, the seal of the composite resin at the tooth/filling margin is compromised and microscopic leakage of bacteria and saliva between the tooth and the filling material can occur. This causes sensitivity at the area of the filling and tooth decay often occurs.
The prior art has attempted to overcome these problems by provision of wedges and matrices formed of materials, such as acrylic or thermoplastic, which are transparent to the curing light for resin material used in dental fillings. These devices allow curing light to be conducted interproximally such that curing takes place between the teeth first.
The prior art transparent wedges tend to experience internal reflection of light directed therethough and, thus, have limited usefulness.